Flea infestation of animals is a health and economic concern for pet owners. In particular, the bites of fleas are a problem for animals maintained as pets because the infestation becomes a source of annoyance not only for the pet but also for the pet owner who may find his or her home generally contaminated with insects. Fleas are known to directly cause a variety of diseases, including allergy, and also carry a variety of infectious agents including, but not limited to, endoparasites (e.g., nematodes, cestodes, trematodes and protozoa), bacteria and viruses. As such, fleas are a problem not only when they are on an animal but also when they are in the general environment of the animal.
The medical importance of flea infestation has prompted the development of reagents capable of controlling flea infestation. Commonly encountered methods to control flea infestation are generally focused on use of insecticides, which are often unsuccessful for one or more of the following reasons: (1) failure of owner compliance (frequent administration is required); (2) behavioral or physiological intolerance of the pet to the pesticide product or means of administration; and (3) the emergence of flea populations resistant to the prescribed dose of pesticide.
Gamma-aminobutyric acid (GABA) is a major neurotransmitter in both insects and vertebrates bound by GABA receptors, which are intrinsic membrane glycoproteins in vertebrate and invertebrate neuronal tissues that are members of the ligand-gated ion channel superfamily of receptors. Researchers have isolated three insect clones encoding putative GABA receptors from Drosophila melanogaster, (1) Rdl (resistance to dieldrin), (2) Grd (GABA and glycine-like receptor of Drosophila); and (3) Lcch3 (ligand-gated chloride channel homologue 3). Insect GABA receptor is a known target of various insecticides including cyclodienes such as dieldrin, and phenylpyrazoles such as fipronil; see for example Casida, J. E., 1993, Archives of Insect Biochem. and Physiol. 22:13-23, and Cole et al., 1993, Pesticide Biochem. and Physiol., 46:47-54. In several insects, including Drosophila, beetles, mosquito, whitefly, cockroach and aphids, resistance to cyclodienes has been linked to a single amino acid mutation from alanine to serine.
Prior investigations have described certain insect GABA receptor subunit protein and/or nucleic acid sequences, including for example, ffrench-Constant et al. 1991, Proc. Nat. Acad. Sci. 88:7209-7213, as well certain vertebrate protein and/or nucleic acid sequences, including for example, Pritchett et al. 1989, Nature, 338:582-585. Unfortunately, many insecticides that target GABA receptors also act on the GABAA receptors of mammals, therefore creating difficulties in using the GABA receptor as a target to kill fleas. Due to the necessity of limiting potential cross-reactivity against the GABA receptors of the animal to be treated, it would be a distinct advantage to have the sequence of the flea GABA receptor, in order to create treatments which are efficacious against fleas while minimizing toxicity to the host animal.
Therefore, isolation and sequencing of flea GABA receptor subunit genes may be critical for use in identifying specific agents for treating animals for flea infestation.